This invention relates to undercarriages for mounting dual wheels, particularly undercarriages suitable for large transport vehicles.
In order to save handling costs, large transport vehicles have been developed that are capable of loading themselves quickly. One such known vehicle is manufactured by CTEC Corporation of Bellevue, Wash. This vehicle has eight lines of axles with the centre two lines acting as driving axles which do not steer. The remaining lines of axles are divided into pairs of half axles and they are used to steer the vehicle as well as to carry the load. Each half axle consists of a short axle on which a set of dual wheels is mounted. Each half axle or short axle is mounted on a retractable undercarriage that has its own individual turntable for steering purposes. A hydraulic cylinder mechanism is able to lower or raise each set of dual wheels relative to the mainframe of the vehicle for loading purposes. With the wheels in a raised or retracted position, the vehicle can be backed under an elevated loading ramp on which the intended cargo has been placed. By extending the wheels and thereby raising the load carrying surface of the vehicle, this surface can be brought into contact with the load to be transported. Once the vehicle has lifted the load from the loading platform, it can then be driven away with its wheels still in the extended or lower position.
Difficulties have been encountered in maintaining and servicing these vehicles which are fairly expensive. One difficulty that has arisen concerns the pivot pins used to mount the hydraulic cylinder mechanism which is used to extend or retract each set of dual wheels. With the known means for mounting these pivot pins which are quite large because of the loads that they must carry, the pins tend to jam or seize in their mounting blocks and this makes the pins considerably difficult to remove.
Another difficulty with the known retractable undercarriage is the knee-joint connection between the arm on which the dual wheels are mounted and the vertical leg of the undercarriage to which the arm is connected at its front end. The known vehicles employ a simple pin-type connection and a spherical thrust bearing between each arm and its respective vertical leg. It will be appreciated this joint is under considerable stress for several reasons including the fact that these vehicles are intended to carry large heavy loads and the joint must also be capable of turning its respective dual wheels in order to steer the vehicle. The known knee-joints in the CTEC vehicles have been subject to premature bearing failure and weldment failure in the arm on which the dual wheels are mounted. The spherical bearings that are used are not designed to take radial loads.
U.S. Pat. No. 3,001,796 issued Sept. 26, 1961 to the Gerstenslager Company describes a retractable undercarriage for a truck trailer, which undercarriage employs a hydraulic cylinder and plunger rod that lower or raise the rear wheels of the trailer. The undercarriage has an arcuate locking channel and a running gear sub-assembly connected to the trailer frame. The running gear assembly is rotatably mounted about the axis of a pivot tube which is disposed between the trailer frame and an outer skirt of the vehicle. A standard clevis pin attaches the top of the hydraulic cylinder to a clevis while the outer end of the plunger rod is connected to a mounting bracket by another standard pin held by cotter pins.
U.S. Pat. No. 4,195,856 issued Apr. 1, 1982 to Oshkosh Truck Corporation, describes a high-lift tag axle for a concrete mixing vehicle. The tag axle is pivoted by means of a generally L-shaped beam which is connected at its forward end to a hydraulic cylinder mechanism that extends generally horizontally. The front and closed end of the hydraulic cylinder is mounted on a short shaft with an expanded head about which a mounting ring of the cylinder is arranged. The shaft is carried by a mounting plate bolted to the vehicle frame. A bolt forms a pivot pin for the outer end of the plunger rod. This bolt is supported in a conventional spherical bearing assembly and is held in place by a nut.
It is an object of this invention to provide a reliable retractable undercarriage for dual wheels that is in inexpensive and easier to maintain.
It is a further object of this invention to provide an undercarriage for dual wheels that is suitable for a vehicle carrying heavy loads and that is less likely to break or fail.